Thin substrates, such as those used for magnetic disks, normally require high vacuum processing. This processing generally involves heating of the substrate to a desired temperature and applying different coatings by sputtering or similar physical vapor deposition processes. The high vacuum processes facilitate very high polarity coating depositions and the achievement of a variety of properties that are controlled by such parameters as background pressure, coating rate, and substrate temperature.
Control of substrate temperature in an evacuated environment (i.e., vacuum) is an important task. Typically, heating of a substrate is performed by radiation transfer from such devices as quartz lamps. However, normal heat conduction processes work very poorly in the vacuum environment. The atmosphere is not present to supply an ambient environment around the heat sink.
During substrate (or disk) processing, it is also often desirable to lower the substrate temperature. For example, controlled cooling of the substrate may be necessary to achieve a desired temperature for a serial coating step, such as chromium, cobalt alloy or carbon layers with magnetic disks. In this instance, the properties of the high hardness, abrasion resistant carbon coatings are enhanced when deposited onto a substrate which is at a relatively low temperature.
Further, cooling of substrates or disks by exposure to the atmosphere while still hot severely limit the usefulness of such substrates or disks for particular applications. Additionally, uncontrolled cooling and/or cooling in atmosphere can adversely affect coating quality by virtue of the diffusion of different coatings at elevated temperature.
Some prior art techniques to cool the relatively thin substrates during processing have used a heat exchanging body designed and configured to be in contact with the article to be cooled. The main disadvantage of such a system is that the act of touching such a relatively thin substrate may do harm to one or more surfaces that have to be maintained in pristine condition. Further, the low mass and the need to handle the substrates only at their edges make them difficult to conductively couple with a heat sink.
To overcome these problems, certain systems have been created to cool thin substrates without any contact to either surface. In these systems, a cooling chamber is provided with stationary heat sinks spaced a predetermined distance apart. The substrate is positioned between these stationary heat sinks and a high thermal conductivity gas is then introduced, filing the entire chamber to the desired operating pressure. The substrate is then cooled to a given temperature, depending on the heat sink temperature, original substrate temperature, gas thermal conductivity, pressure, and spacing between the substrate and heat sinks.
However, the process steps of multiple thin film depositions and heating substrates have been changed to employ higher target temperatures before cooling. Furthermore, newer products have thicker substrates and require higher cooling rates before an overcoat process. Providing the required cooling for such products will lower the production rate per hour compared to that achieved in processing of older products using current cooling techniques. Therefore, an improved cooling system is needed to meet the overcoat process specification with a higher throughput.